Assigning new numbers to display elements of an autostereoscopic display

ABSTRACT

A processor system and computer-implemented method are provided for assigning view numbers to display elements of an autostereoscopic display for use in interleaving image data of different viewpoints of a scene on the basis of said assigned view numbers. The assignment is performed in an efficient yet accurate manner and may be easily adapted to different optical designs of such autostereoscopic displays, for example, in terms of pitch and/or slant of the optical elements used in such autostereoscopic displays, or to different sub-pixel layouts of the display panel.

FIELD OF THE INVENTION

The invention relates to a computer-implemented method and a processorsystem for assigning view numbers to display elements of anautostereoscopic display. The invention further relates to a computerreadable medium comprising instructions arranged to cause a processorsystem to perform the computer-implemented method.

BACKGROUND ART

Increasingly, display devices such as televisions, digital photo frames,tablets and smartphones comprise 3D displays to provide a user with aperception of depth when viewing content on such a device, for examplefor in home or portable entertainment, medical imaging or computer-aideddesign (CAD). For that purpose, such 3D display devices may, either bythemselves or together with glasses worn by the user, provide the userwith different images in each eye to provide the user with a perceptionof depth based on stereoscopy, i.e., a stereoscopic perception of depth.

3D display devices typically use content which contains depthinformation in order to establish the content on screen as having adegree of depth. The depth information may be provided implicitly in thecontent. For example, in the case of so-termed stereoscopic content, thedepth information is provided by the differences between a left and aright image signal of the stereo content. Together, the left and rightimage signal thus constitute a stereoscopic 3D image signal. The depthinformation may also be provided explicitly in the content. For example,in content encoded in the so-termed image+depth format, the depthinformation is provided by a 2D depth signal comprising depth valueswhich are indicative of distances that objects within the 2D imagesignal have towards a camera or viewer. Instead of depth values, alsodisparity values may be used, e.g., the 2D depth signal may be a 2Ddisparity signal, or in general, a 2D depth-related signal. Techniquesare known to generate a 2D depth-related signal from a stereo 3D imagesignal, e.g., for view synthesis for autostereoscopic displays. Ingeneral, the data representing content containing depth information isin the following also simply referred to as ‘3D image data’.

Autostereoscopic displays provide stereoscopic perception of depthwithout needing the viewer to wear polarized, color-filter-based orshutter-based glasses. For that purpose, optical components are used,such as lenticular lens arrays (or more general lenticular or barriermeans), which enable the display to emit a viewing cone from each givenpoint on the 3D display, the viewing cone comprising at least a leftview and a right view of a scene. This enables the viewer to see adifferent image with each eye when positioned accordingly within theviewing cone. Certain types of autostereoscopic displays, sometimesspecifically referred to as ‘automultiscopic’ displays, provide a seriesof views of a scene represented by the 3D image data to a viewer in whatis typically referred to as a viewing cone. This allows the viewer toassume multiple positions in the viewing cone, e.g., to experienceexperiencing motion parallax while still obtaining a stereoscopicperception of the scene. Some displays may emit such series of views ineach of a series of repeated viewing cones.

Examples of such autostereoscopic displays are described in a paper byC. van Berkel et al. entitled “Multiview 3D—LCD” published in SPIEProceedings Vol. 2653, 1996, pages 32 to 39 and in GB-A-2196166. Inthese examples the autostereoscopic display comprises a matrix LC(liquid crystal) display panel which has rows and columns of pixels(display elements) and which acts as a spatial light modulator tomodulate light from a light source. The display panel may be of the kindused in other display applications, for example computer display screensfor presenting display information in two-dimensional form. A lenticularsheet, for example in the form of a molded or machined sheet of polymermaterial, may overlay the output side of the display panel with itslenticular elements, comprising (semi) cylindrical lens elements,extending in the column direction with each lenticular element beingassociated with a respective group of two, or more, adjacent columns ofdisplay elements and extending in a plane that runs parallel with thedisplay element columns.

U.S. Pat. No. 6,064,424 also describes an example of an autostereoscopicdisplay with an array of parallel lenticular elements overlying thedisplay, in which the lenticular elements are slanted with respect tothe display pixel columns. It is said that the reduction in displayresolution experienced in such apparatus, particularly in the case of amulti-view type display, is shared between both horizontal and verticalresolution.

To display content on an autostereoscopic display having an array oflenticular elements, an output image may be generated by theautostereoscopic display or a device connected thereto on the basis ofthe 3D image data. This may involve a ‘interleaving’, ‘weaving’ or‘interdigitation’ step in which it is determined for each displayelement of the display which image data from which view is to bedisplayed by the display element, with the output image then beinggenerated by selecting the image data from the corresponding view fordisplay by the respective display element. Here, the term ‘displayelement’ may include pixels but also sub-pixels. Such ‘interleaving’,‘weaving’ or ‘interdigitation’ is in the following simply referred to as‘interleaving’.

For example, the aforementioned U.S. Pat. No. 6,064,424 describes thatthe individually operable display elements of the display are driven inan appropriate manner such that a narrow slice of a 2D image isdisplayed by selected display elements under an associated lenticule.The display produced by the panel comprises six interleaved 2Dsub-images constituted by the outputs from respective display elements.Each lenticule 16 provides six output beams from the associatedunderlying display elements with view-numbers 1 to 6 respectively whoseoptical axes are in mutually different directions and angularly spreadaround the longitudinal axis of the lenticule.

In general, such interleaving is also known from other publications, forexample from U.S. Pat. No. 7,616,227 which describes a system and methodfor interdigitating multiple perspective views in a stereoscopic imageviewing system, and from U.S. Pat. No. 7,375,886, which describes amethod and apparatus for optimizing viewing distance for a stereogramsystem in which optimum pitch values are stored in a table for specifiedviewing distances and an interdigitation program then acts on the tablevalues and creates a mapping of interdigitated views for each viewingdistance.

WO 2015/091014 describes characterizing a lenticular lens sheet using apitch and slant, and to determine a phase for the discrete positions ofdisplay elements with respect to the periodic lenticular lens based onthe pitch and slant.

SUMMARY OF THE INVENTION

One of the objects of the invention is to obtain a computer-implementedmethod and processor system for assigning view numbers to displayelements of an autostereoscopic display in an efficient yet accuratemanner. The view numbers which are assigned by the method or system maythen be used for interleaving image data of different viewpoints of ascene on the basis of the assigned view numbers.

The following measures relate to an autostereoscopic display comprising:

-   -   a display panel comprising an array of display elements; and    -   an array of elongated optical elements for redirecting light        emitted by the display elements in mutually different        directions, the optical elements being arranged substantially in        parallel at a pitch distance p and oriented with their main        longitudinal axis at a slant s to a column direction of the        array of display elements.

Such autostereoscopic displays are known per se. For example, as lightredirecting optical elements, a lenticular lens array or a barrier-typearray may be used.

A first aspect of the invention provides a computer-implemented methodof assigning view numbers to display elements of an autostereoscopicdisplay for use in interleaving image data of different viewpoints of ascene on the basis of said assigned view numbers. The method comprises:

-   -   determining a phase for a respective display element to be used        in the assignment of the view number, wherein the phase is        representative of a relative horizontal position of the        respective display element with respect to an optical element        redirecting the light emitted by the respective display element        and is thereby indicative of a direction in which the light is        redirected, wherein the phase is determined as a delta with        respect to the phase of a preceding display element at a        horizontal position x and a vertical position y in the array of        display elements in accordance with:

phase(x+1,y)=(phase(x,y)+h)% t

phase(x,y+1)=(phase(x,y)+v)% t

wherein h represents a horizontal delta in phase per display element,wherein v represents a vertical delta in phase per display element,wherein t represents a total number of phases and wherein % is afunctional representation of a modulo operation, wherein values of h, vand t are selected as integer values which approximate the pitchdistance p and the slant s in accordance with

$p \approx {{\frac{t}{h}}\mspace{14mu}{and}\mspace{14mu} s} \approx \frac{v}{h}$

so that the approximation error in the phase over the width and heightof the array of display elements accumulates to less than the pitchdistance p; and

-   -   determining the view number from said determined phase based on        a number of most significant digits of a numerical        representation of the phase.

A further aspect of the invention provides a computer readable mediumcomprising transitory or non-transitory data representing instructionsfor a processor system to perform the method.

A further aspect of the invention provides a processor system forassigning view numbers to display elements of an autostereoscopicdisplay for use in interleaving image data of different viewpoints of ascene on the basis of said assigned view numbers. The processor systemcomprises:

-   -   a memory comprising instruction data representing a set of        instructions;    -   a processor configured to communicate with the memory and to        execute the set of instructions, wherein the set of        instructions, when executed by the processor, cause the        processor to determine a phase for a respective display element        to be used in the assignment of the view number, wherein the        phase is representative of a relative horizontal position of the        respective display element with respect to an optical element        redirecting the light emitted by the respective display element        and is thereby indicative of a direction in which the light is        redirected, wherein the phase is determined as a delta with        respect to the phase of a preceding display element at a        horizontal position x and a vertical position y in the array of        display elements in accordance with:

phase(x+1,y)=(phase(x,y)+h)% t

phase(x,y+1)=(phase(x,y)+v)% t

wherein h represents a horizontal delta in phase per display element,wherein v represents a vertical delta in phase per display element,wherein t represents a total number of phases and wherein % is afunctional representation of a modulo operation, wherein values of h, vand t are selected as integer values which approximate the pitchdistance p and the slant s in accordance with

$p \approx {{\frac{t}{h}}\mspace{14mu}{and}\mspace{14mu} s} \approx \frac{v}{h}$

so that the approximation error in the phase over the width and heightof the array of display elements accumulates to less than the pitchdistance p; and

determine the view number from said determined phase based on a numberof most significant digits of a numerical representation of the phase.

The above measures involve assigning view numbers to display elements ofan autostereoscopic display for use in interleaving image data ofdifferent viewpoints of a scene on the basis of said assigned viewnumbers. Such type of interleaving is known per se, e.g., as indicatedin the background section, and generally involves assigning a viewnumber to each respective display elements and then suitablyinterleaving the image data of the different views to ensure that thelight emitted by the display in the different angular directionscorresponds to the different views.

The assigning of view numbers to display elements typically results in a‘semi-regular’ spatial pattern for each view number which may be used tosub-sample the image data of the respective view, e.g., if the imagedata is available at a higher resolution, to interpolate the image data,e.g., if the image data is sampled at a different sampling grid, or toselectively generate the image data, e.g., by known view rendering orview synthesis techniques. In general, once view numbers have beenassigned to display elements, it is known how to suitably generate aninterleaved output image.

Such interleaving normally takes into account the type of lenticularlens array and its configuration in the display, which may include theslant of the lenticular lens array with respect to the display panel andthe pitch distance between lenticular elements. The slant may beexpressed as or in relation to the angle of the main longitudinal axisof the lenticular elements to the column direction of the array ofdisplay elements but may also be expressed differently, e.g., inrelation to the row direction of the array of display elements. Theslant may be expressed in degrees, radians, etc., but is commonlyexpressed by reference to triangle trigonometry, e.g., by indicating thehypotenuse of a triangle. For example, ⅙ may refer to the hypotenusefrom display element (n, m) to display element (n+1, m+6) and the slantangle corresponding to arctan ⅙≈10 degrees in case the display elementshave a 1:1 aspect ratio in horizontal and vertical direction. The pitchdistance, or simply ‘pitch’, may be expressed in as an absolute number,e.g., in millimeters, but is commonly expressed in relation to thedisplay panel, e.g., by a number of display elements, e.g., a number ofpixels. For example, the pitch may be 1½ pixels. The pitch betweenoptical elements may be measured horizontally but also in a differentdirection, e.g., in a direction perpendicular to the slanted elongatedoptical elements.

It is noted that in the above and following, the term ‘display element’typically refers to a pixel but may also include a group of pixels or asub-pixel.

The above measures provide an efficient yet accurate way of determiningthe view number of each display element, namely by assigning a phase toeach display element. Here, the phase represents the relative horizontalposition of the respective display element with respect to an opticalelement which redirects the light emitted by the respective displayelement. As such, the phase is indicative of a direction in which thelight is redirected, and ultimately indicative of the view number whichis to be assigned to the particular display element. Assigning the phasemay involve calculating the phase for a display element located at aposition (x, y) in the array of display elements on the basis of thepitch p and slant s of the array of optical elements. For example, thephase may be calculated as x/p+y*s, which calculation may involve adivision per display element and a numerical representation as afloating-point number.

Instead of the above-described calculations, the above measuresintroduce a [h,v,t] notation which defines the phase of a displayelement relative to the phase of a preceding display element, namelyphase(x+1, y)=(phase(x, y)+h) % t and phase(x, y+1)=(phase(x, y)+v) % t,where x represents a horizontal position in the array of displayelements, y represents a vertical position in the array of displayelements, h represents a horizontal delta, v represents a verticaldelta, t represents the total number of phases and % t is a functionalrepresentation of a modulo operation, e.g., a ‘true’ modulo or a checkagainst 0 and t which is then possibly followed by anincrement/decrement by t. The use of such a [h,v,t] approach involvestranslating the values of the pitch p and the slant s into thehorizontal phase offset h and the vertical phase offset v, for exampleon the basis of p=|t/h| and s=v/h. This calculation may be performed‘once’ for a particular type and/or a particular configuration of theautostereoscopic display, instead of having to be performed for eachdisplay element.

Disadvantageously, the assigning of phases in the above-describedrelative manner based on the [h,v,t] approach may require a highnumerical accuracy for calculating and storing the values of h, v, t andthe phase. If only a limited numerical accuracy is used, e.g., aninteger representation, only a limited number of different slants and/orpitches may be expressed using the [h,v,t] notation, which may beinsufficient in certain situations. For example, due to manufacturinginaccuracies, the actual pitch and/or slant may deviate slightly fromtheir nominal value. Another example is that the process of controllingthe rotational position of the lenticular lens array during manufactureof the autostereoscopic display may be slightly inaccurate, leading to aslight deviation from the intended slant. Yet another example is thatdue to ‘view distance adjustment’ (also discussed later), a slightlydifferent pitch may be assumed in the view number assignment so as toeffect the view distance adjustment.

In the example of [6, 1, 9], the next representable pitch by incrementof t is [6, 1, 10], achieving only a step of ⅙ in pitch. Yet anotherexample is that in the above-described assigning of phases, inaccuraciesdue to the accumulation of rounding errors may occur, which may beparticularly relevant for high-resolution display panels, e.g., 4K or 8Kor even higher resolution displays having many display elements.

To address the above problem of the usage of [h,v,t], the values of h, vand t may be selected as integer values which approximate the pitchdistance p and the slant s in accordance with

$p \approx {{\frac{t}{h}}\mspace{14mu}{and}\mspace{14mu} s} \approx \frac{v}{h}$

so that the accumulated approximation error in the phase over the widthand height of the array of display elements is less than the pitchdistance p. In other words, an integer representation of h, v and t maybe selected such that the values sufficiently approximate the pitchdistance p and the slant s, and in particular, such that the accumulatedapproximation error in the phase over the entire pixel grid is less thanthe pitch distance p. To enable such comparison, the pitch distance pmay be expressed as a phase difference, or in general, the approximationerror and the pitch distance p may be expressed as a same type of unit.

The approximation error itself may be expressed with respect to aselection of values of h, v, and t which accurately represents the pitchdistance p and the slant s in accordance with

$p \approx {{\frac{t}{h}}\mspace{14mu}{and}\mspace{14mu} s} \approx \frac{v}{h}$

and thereby represents a reference for the earlier mentionedapproximation by integer values. Accordingly, the accumulatedapproximation error may be easily numerically calculated for aparticular selection of h, v, and t. The pitch distance p may representa phase difference between display elements which are associated with asame or similar view in adjacent viewing cones, and may therebyconsidered to represent the phase difference between adjacent viewingcones. This may be considered as a minimum accuracy for the earliermentioned approximation by integer values. In some embodiments, thevalues of h, v and t may be selected so that the accumulatedapproximation error is less than 75% of the phase difference of thepitch distance p, or less than 50% of the phase difference, or less than25%, or less than 10%.

The integer values of h, v and t may be calculated in various ways.

For example, the slant s and the pitch distance p may be approximated asrational numbers having a common denominator, with the values of h, vand t then being obtained as, respectively, the value of the commondenominator, a rounded multiplication result of multiplying s by h, anda rounded multiplication result of multiplying p by h. Each of thevalues of h, v, and t may thus be represented by an integer numberinstead of a floating-point number. This may effectively represent an‘upscaling’ of the number of phases, e.g., from 9 to 18 phases or to aneven higher number, and a corresponding determination of the values ofthe horizontal delta h and the vertical delta v in the ‘upscaled’domain. Thereby, a phase calculation which uses an integerrepresentation of [h,v,t] may still provide sufficient accuracy indetermining the phase of a display element. Another example is that a[1.0, s, p] notation may be used in which s and p are the actual slantand pitch values expressed as floating-point numbers, which may beupscaled by a factor a and then rounded to obtain [a, round(a*s),round(a*p)], which would then correspond to [h, v, t]. In general, thevalue for t may be selected first, for example based on a desiredprecision, after which the value of h may be determined as a function oft and h, after which the value of v may be determined as a function of hand s, and as an optional last step, if h and v are deemed to be toolarge, e.g., requiring the numerical representation of the phase to beable to store very large values, scaling the values of h, v, and t downby a same factor

Using the ‘upscaled’ phase in the above manner, the view number may thenbe determined from the phase based on a number of most significantdigits of the numerical representation of the phase. Here, ‘based on’includes the view number being directly determined as a number of mostsignificant digits, e.g., by a zero-fill right-shift operation, but alsoincludes other ways of determining the view number based on the mostsignificant digits, e.g., by using these as an index to a look-up table.

In accordance with the above measures, the view number may be assignedin a computationally efficient manner, for example by iterativelyproceeding through the rows and columns of display elements anddetermining the phase of a respective display element in accordance withthe above relative phase relations. Various configurations of lenticularlens arrays may be characterized by the [h,v,t] notation. For example, adisplay having optics characterized by pitch 1½ and slant ⅙ may berepresented by [6, 1, 9], and the pitch 5/3 and slant ⅓ may berepresented as [3, 1, 5].

This allows accurate determination of the view number while maintaininga low computational complexity, allowing various values of the slantand/or pitch to be taken into account and/or reducing rounding errors,in particular larger errors caused by the repeated accumulation ofsmaller rounding errors. The latter may be particularly relevant forhigher resolution displays, e.g., the aforementioned 4K or 8K displays.

Optionally, the value of the common denominator or h, the value of v orthe value of t may be selected as or near a maximum value of thenumerical representation of the phase, for example as 65535 for a 16-bitnumerical representation of the phase. Thereby, various pitch and slantconfigurations may be represented with a relatively high accuracy. Insome embodiments, the value of h, the value of v and the value of t maybe jointly selected so that a largest one of said values is at or nearthe maximum value of the numerical representation of the phase. In someembodiments, the value of h, the value of v and the value of t may bejointly selected so that a largest one of said values is near themaximum value of the numerical representation of the phase, whileallocating a headroom with respect to the maximum value for allowingadjustments of t. In other words, the value of h, the value of v and thevalue of t may be selected so that a largest one of said values plus aheadroom value equals the maximum value of the numerical representationof the phase, wherein the headroom value may represent an allocation ofa headroom with respect the maximal value for allowing adjustments of t.This enables so-called view distance adjustment, by which the value of tmay be adjusted to adjust for the view distance of a viewer to theautostereoscopic display. The headroom may for example be selected toallow the view distance adjustment to be performed within a particularrange. For example, if the view distance adjustment may maximally causean increase in a nominal value of t by 321, and if the value of t is thelargest value, the value of t may be selected to be 65535−321=65214. Theterm ‘near’ may thus refer to a maximum within the numericalrepresentation of the phase subject to an allocation of headroom foradjustment of t for view distance adjustment.

Optionally, the display elements may be pixels or group of pixels, eachpixel may comprise a number of sub-pixels, and a sub-pixel phase may beassigned to a respective sub-pixel by adding an offset to, orsubtracting an offset from, the determined phase of the pixel or thegroup of pixels. As such, the phase may be determined using the [h,v,t]approach for each pixel or group of pixels, with the phase of asub-pixel then being determined by adding an offset to, or subtractingan offset from, the determined phase. For example, the determined pixelphase may be assigned to a selected geometric position within thepixel's surface, and the sub-pixel phases may be determined by adding orsubtracting respective offsets which represent the difference in theirgeometric position with respect to the selected geometric position. Suchadding or subtracting of offsets may be performed in an iterativemanner, e.g., by repeatedly adding or subtracting an offset and therebyproceeding through the sub-pixels. It is noted that since any roundingerror in the sub-pixel phase offsets may, if at all, only accumulateacross the few sub-pixels, the sub-pixel phase offset may be representedin reduced precision, for example in the same number of (mostsignificant) bits of the phase which are used to determine the viewnumber. As will also be elucidated in the detailed description, such anapproach may also provide more flexibility in terms of supportingdifferent sub-pixel arrangements (layouts).

Optionally, determining the view number from the determined phase maycomprise using the number of most significant digits of the numericalrepresentation of the phase as an argument to a function providing amapping from the determined phase to the view number, such as an indexto a look-up table. Such a function may provide flexibility in terms ofmapping, as different mapping functions may be defined by way of such afunction. In a specific example, such a function may be implemented byloading appropriate values into the look-up table. For example, thelook-up table may define stereoscopic regions and pseudoscopic regionsin a viewing cone of the autostereoscopic display by comprising, forincreasing phases, a stereoscopic sequence of views in which the viewnumbers increase and a pseudoscopic sequence of views in which the viewnumbers decrease. In such and other embodiments, the pseudoscopicsequence of views may consist of a subset of the view numbers of thestereoscopic sequence of views.

Optionally, the look-up table contains integer representations of theview numbers. Optionally, the entries in the look-up table may beinterpolated during look-up. For example, if a particular phase is notcomprised in the look-up table, the view number may be interpolated as afunction of the view numbers of two adjacent phases, for example, usinga weighted interpolation in which the weights are determined inverselyproportionate with the distance to a respective adjacent phase.

In general, the processor system may be implemented as an integratedcircuit, such as a system-on-chip. In general, the autostereoscopicdisplay may comprise the processor system, e.g., as an internalcomponent.

It will be appreciated by those skilled in the art that two or more ofthe above-mentioned embodiments, implementations, and/or aspects of theinvention may be combined in any way deemed useful.

Modifications and variations of the method which correspond to thedescribed modifications and variations of the integrated circuit can becarried out by a person skilled in the art on the basis of the presentdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter. Inthe drawings,

FIG. 1 shows a processor system and a 3D display for adjacently emittinga series of views in each of a series of viewing cones, with theprocessor system generating and providing an interleaved output image tothe 3D display for display;

FIG. 2A illustrates the assigning of phases to display elements of the3D display on the basis of a [h,v,t] approach for a 3D display having 9assignable phases, e.g., for views or fractional views, pitch distance pof 1½ pixel and slant angles of ⅙;

FIG. 2B illustrates the display of interleaved image data of views;

FIG. 2C illustrates the assigning of phases to display elements similarto FIG. 2A but with a higher-accuracy phase representation having 64214phases;

FIG. 3 illustrates a mapping of phase to view number in which themapping provides a stereoscopic sequence of views and a pseudoscopicsequence of views;

FIG. 4 shows the 3D display comprising the processor system;

FIG. 5 shows a method of processing 3D image data; and

FIG. 6 shows a computer readable medium comprising non-transitory datarepresenting instructions for a processor system to perform the method.

It should be noted that items which have the same reference numbers indifferent Figures, have the same structural features and the samefunctions, or are the same signals. Where the function and/or structureof such an item has been explained, there is no necessity for repeatedexplanation thereof in the detailed description.

LIST OF REFERENCE AND ABBREVIATIONS

The following list of references and abbreviations is provided forfacilitating the interpretation of the drawings and shall not beconstrued as limiting the claims.

-   -   0-5 series of views    -   100 series of repeated viewing cones    -   102-106 viewing cones    -   110 stereoscopic viewing position    -   112 pseudoscopic viewing position    -   120 processor system    -   122 interleaved output image    -   130 processor    -   135 memory    -   140 3D display    -   142 display panel    -   144 lenticular lens array    -   200 array of pixels with subpixels showing assigned phases    -   210 pixel at pixel position (1,0)    -   220 pixel at pixel position (0,1)    -   230 pixel at pixel position (0,0)    -   260 interleaved image data of views    -   280 sub-pixels with assigned phases    -   300 graph showing phase-to-view-number mapping    -   310 phase    -   320 view number    -   330 phase-to-view-number mapping    -   340 stereoscopic sequence of views    -   350 pseudoscopic sequence of views    -   400 method of assigning view numbers    -   410 determining phase for display element    -   420 determining view number from determined phase    -   450 computer readable medium    -   460 non-transitory data representing instructions

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a processor system 120 which is connected to a 3D display140 and which may in some embodiments provide an output image, e.g., inthe form of display data 122, to the 3D display. As will also beelucidated with reference to FIG. 4, the processor system 120 may becomprised in an external device which is connected to the 3D display140, such as a set-top box or computer, but may also be comprised in the3D display itself or in a device which includes the 3D display, e.g., atelevision, tablet or smartphone. The 3D display 140 is anautostereoscopic 3D display for enabling stereoscopic viewing of contentdisplayed thereon without a need for the user to wear glasses. For thatpurpose, the 3D display 140 is shown to comprise a light generatingportion 142 which is typically comprised of an array of light emittingor light modulating elements. Such type of elements are also referred toas ‘display elements’. For example, the light generating portion 142 maybe formed by a Liquid Crystal Display (LCD) panel and a backlight, as isknown from the technical field of displays.

The 3D display 140 is further shown to comprise optical means 144 forredirecting light generated by the light generating portion 142 intodifferent directions. Although not shown explicitly in FIG. 1, theoptical means 144 may comprise or consist of an array of elongatedoptical elements, such as lenticular elements or parallax barrier-typeelements. The light generating portion 142 may be suitably arranged andcooperative with the optical means 144 such that a series of views 0-5are emitted from the 3D display 140 in the form of a viewing cone 104.The series of views 0-5 may show a series of images. Thus, the viewerwill perceive, when viewing one of the series of views 0-5, a respectiveone of the series of images. The series of images may, in terms of imagecontent, correspond to a camera facing a scene and moving from left toright in front of, and relative to, said scene. As such, a viewerpositioned at viewing position 110 within the viewing cone 104 mayperceive two different ones 2, 3 of the series of views 0-5 and maythereby obtain stereoscopic viewing of said scene. Conversely, a viewerpositioned at viewing position 112 may perceive so-called pseudoscopicviewing, which will be further explained with reference to FIG. 3.

It is noted that 3D displays of the above configuration, and the mannerof processing a series of images for display as the series of views 104,are in itself known. For example, U.S. Pat. No. 6,064,424 discloses anautostereoscopic display apparatus having lenticular elements as opticalmeans and discusses the relationship between display elements and thelenticular elements. U.S. Pat. No. 6,064,424 also discloses that theelongated optical elements may be arranged substantially in parallel ata pitch distance p and oriented with their main longitudinal axis at aslant angle s to a column direction of the array of display elements.Such and other parameters characterizing the elongated optical elementsare in the following also referred to as ‘optical designs’.

It is desirable for a processor system generating interleaved displaydata for an autostereoscopic display to support a variety of suchoptical designs. The variety in optical designs may increase with anincrease in prevalence of autostereoscopic displays. For example, it maybe desirable to support a pitch 1½ and slant ⅙ design next to a pitch5/3 and slant ⅓ design for a vertically striped pixel grid, or opticaldesigns for other pixels grids such as a horizontally striped pixel grid(when for example using a vertically striped pixel grid panel inportrait mode), or other pixel grids such as Pentile RGBW(https://en.wikipedia.org/wiki/PenTile matrix family#PenTile RGBW).

The optical designs may be adapted to adjust to applicationrequirements. For example, a larger pitch may be used to ‘trade-off’more of the display panel resolution for depth. Moreover, in practice,deviations from the theoretical design may occur, as a result from,e.g., manufacturing tolerances. As a result, the actual pitch maydeviate from its theoretically designed value, for example due to theaforementioned manufacturing tolerances, or the wish for user-controlledviewing distance adjustment. Another example is that the actual slantmay deviate due to there being less space for alignment with the displayelements due to the ever-smaller bezels of displays.

It may thus be desirable to be able to support a variety of differentpitch and slant values, and/or different pixel grids, while still usingan efficient implementation. The latter may imply using integer-basednumerical representations of parameters and variables, rather than,e.g., floating-point based numerical representations.

The following describes, by way of example, the interleaving of imagedata by determining the phase for each pixel and then sub-pixel, whichmay take so-called ‘view distance correction’ into account, and thenassigning a view number to each sub-pixel based on the phase, forexample, by determining which of a number of views that have beenrendered beforehand best corresponds to the determined phase.

Determining the Phase

FIG. 2A illustrates the assigning of phases to display elements of the3D display on the basis of a [h,v,t] approach for a 3D display having 9assignable phases, corresponding for example to separate views orfractional views of the 3D display, and the 3D display having a pitchdistance p of 1½ and a slant angle s of ⅙. Specifically, FIG. 2A shows apixel grid 200 in which each pixel consists of three sub-pixels arrangedin a vertically striped pixel grid, e.g., a R(ed), G(reen) and B(lue)sub-pixel. In the example of FIG. 2A, a number of pixels 210-230 areexplicitly indicated by bounding boxes around their respectivesub-pixels while other pixels are not explicitly indicated.

It may be desired to compute a phase for each individual sub-pixel. Forthat purpose, the following examples first determine the phase of apixel, henceforth also referred to as pixel phase (or ‘pixelPhase’) andthen assign phases to the pixel's sub-pixels, henceforth also referredto as sub-pixel phases (or ‘subpixelPhase’). In alternative embodiments,the determined pixel phase may be simply assigned to all sub-pixels. Inother embodiments, it is conceived that the phase is directly determinedfor each sub-pixel in the manner as described in the following for pixelphases.

Using the [h,v,t] approach, the phase relation in the FIG. 2A examplemay, from one pixel to the next pixel in a horizontal direction,correspond to:

pixelPhase(x+1,y)=(pixelPhase(x,y)+6)%9

This relation is visually indicated in FIG. 2A by the arrow labeled ‘+h,% t’ between pixel 230 at position (0, 0) and pixel 210 at position (1,0), with the value of h being in this example ‘6’ and the value of tbeing in this example ‘9’.

Similarly, the phase relation from one pixel to the next pixel in avertical direction may correspond to:

pixelPhase(x,y+1)=(pixelPhase(x,y)+1)%9

This relation is visually indicated in FIG. 2A by the arrow labeled ‘+v,% t’ between pixel 230 at position (0, 0) and pixel 220 at position (0,1), with the value of v being in this example ‘1’ and the value of tbeing in this example ‘9’.

Having determined the pixel phase, the phase for the sub-pixels may becomputed by adding phase offsets which characterize the sub-pixellayout, for example, for each sub-pixel i:subPixelPhase(x,y,i)=pixelPhase(x,y)+phaseOffset(i).

The sub-pixel phases may be determined by taking their relativegeometric position within the pixel's surface area into account, andthereby the relative geometric position with respect to (overlaying)optical elements. For example, the determined pixel phase may beassigned to the upper-left corner of a pixel. In this example, thesub-pixel phase offsets in the pixel grid of FIG. 2A may correspond toh/6+v/2, h/2+v/2 and 5h/6+v/2. However, as also illustrated in FIG. 2A,one may also assign the pixel phase to the center of the left-mostsub-pixel. In this example, the sub-pixel phase offsets may be 0, h/3and 2h/3, or 0, 2 and 4 in the FIG. 2A example. FIG. 2A illustrates thelatter example by showing the assigned phase for each of the sub-pixels.

The use of sub-pixel phase offsets allows for the sub-pixel phases to beeasily calculated for different sub-pixel grids on the basis of thepixel phase. For example, if the sub-pixels within a pixel would beoriented as horizontal stripes rather than the vertical stripes shown inFIG. 2A (for example when using the panel of FIG. 2A in a portraitconfiguration) and the pixel phase is assigned to the center of thetop-most sub-pixel of each pixel, the sub-pixel phase offsets may be 0,v/3 and 2v/3.

It is noted that the offsets 0, ⅓ and ⅔ (corresponding to thegeometrical location of a sub-pixel within a pixel) in the two examplesabove are in principle independent of the pitch and the slant, and assuch characterize the sub-pixel phases in a manner that can easilyaccommodate varying values for the pitch and the slant.

In some cases, the sub-pixel grid may not be defined by sub-pixeloffsets of within a pixel, for example, if the (sub)pixel grid is not anorthogonal grid. In that case, sub-pixel offsets may be defined for agroup of pixels which does repeat across the display panel. For example,for a Pentile RGBW sub-pixel grid, the RGBW offsets for the sub-pixelsin the even rows may be 0, h/4, h/2 and 3h/4, and h/2, 3h/4, 0 and h/4for the sub-pixels in the odd rows, respectively. Typically, (sub)pixelgrids repeat within 2×2 pixels, so different sub-pixel offsets may bedefined for odd and even rows and odd and even columns, thereby enablinga wide range of (sub)pixel grids to be handled in the assignment ofsub-pixel phases.

Increased Precision

Referring back to the use of the [h,v,t] approach, in general, aselection of values for [h,v,t] may correspond to an optical designhaving pitch |t/h| and slant v/h. Accordingly, an optical design havingpitch 1½ and slant ⅙ may be expressed by [6, 1, 9], or in other words,as a horizontal delta h of ‘6’ in phase per pixel, a vertical deltaoffset v of ‘1’ per line of pixels, and a total number of phases t of‘9’.

This notation, which combines pitch and slant in a rationalrepresentation using the same denominator, may enable the pixel phase tobe easily computed in a scanning manner, e.g., by proceedingsequentially through the pixel grid, using:

pixelPhase(x+1,y)=(pixelPhase(x,y)+h)% t and

pixelPhase(x,y+1)=(pixelPhase(x,y)+v)% t

The [h,v,t] approach further allows increased precision. For example,[6, 1, 9] may be scaled by a factor 2 to the equivalent [12, 2, 18],which still denotes a pitch 1½ and slant ⅙ configuration. But with 18phases instead of 9, deviations in pitch may be more accuratelyrepresented. Namely, for [6, 1, 9], the next representable pitch byincrement oft is [6, 1, 10], resulting in a step of ⅙ in pitch. Incontrast, for [12, 2, 18], the next representable pitch is [12, 2, 19],which is a 1/12^(th) step in pitch and thus half the step size. Byscaling up the representation, finer adjustments can be made.

For example, if the pitch of an optical design turns out to be 1.49963,this pitch may be represented in [h,v,t] as [10000, 1667, 149963] (stillwith a slant of approximately ⅙), or [h,v,t] as [30000, 5000, 3*149963]to obtain s precisely as ⅙.

Another example is that for a 4K display panel, with a pitch around 1½and a slant of around ⅙, it may be desirable to represent h, v and tin16-bit precision, e.g., to prevent accumulation of rounding errorsresulting in too large errors in the phase assignments. For even higherresolution display panels, such as 8K display panels, even moreprecision may be needed as the h/v deltas may be accumulated over longerand more lines. Also, when more resolution is available, it is likelythat more of the display panel resolution will be used for depth ratherthan for sharpness, with this trade-off being known per se, resulting indesigns with larger pitches. Also in this case, more precision may beneeded, e.g., 18 bits for 8K display panels with a pitch around 4. Anunsigned number may be used to represent t, and it may be chosen whichof h and v is represented by a signed number to be able to specify bothnegative and positive slant. For example, it may be preferable torepresent h unsigned, since flipping the sign of h also flips the orderof the phases in a horizontal direction.

For reasons explained further onwards (see also the sections on viewdistance adjustment and the phase-to-view mapping), it may beadvantageous to scale up the [h,v,t] representation such that thenumbers are as large as possible, e.g., within a selected numericalrepresentation. Typically, the ‘scaling factor’ may be determined by thevalue of t, since h usually is smaller than t (since pitches smallerthan 2 do not lead to enough separation between left and right-eye viewsfor more than 2 views) and v is typically around one sixth of h toproperly distribute the horizontal and vertical resolution, and thereby(much) smaller than t. However, in some cases, such as a small pitch anda 45-degree slant, v or h rather than t may determine the scalingfactor.

As an example for the accuracy in representing the slant in this manner:scaling up [6, 1, 9] to 16-bit by multiplying by 65535/9 (using integerdivision) yields [−43686, 7281, 65529]. A 1-off slant, referring to thesmallest possible modification of the slant value without changingpitch, namely a change of 1 of v, may then be represented by [15120,7282, 65529]. Such a [h,v,t] approach would approximately result in anaccumulated rounding error of approximately 0.3 in phase (out of 9) overthe entire pixel grid of a 4K display panel. Typically, this may beconsidered to be sufficiently accurate, providing an acceptable order ofallowable error. Less accuracy may also be acceptable, but it may bedesirable to leave headroom for different optical designs.

The required accuracy of the pitch may be determined by the smalleststeps in change in pitch which are to be supported. Such changes inpitch may need to be supported for various reasons, including so-termedview distance adjustment.

View Distance Adjustment

View distance adjustment refers to an accommodation in the assignment ofphase, and thereby in the assignment of view numbers, for a particularview distance of a viewer to the display which is different from thenominal view distance of the optical design. Such view distanceadjustment may be implemented by slightly adjusting the value of thepitch which is assumed in the phase calculation from a nominal valuerepresenting the actual optical design. Typically, such adjustments inpitch are in the permilles-order. To have sufficient steps inadjustability, for example 100 steps, this may result in an increment oft of 1/10000 or somewhat smaller. Such increments of t results in anadjusted pitch p in view of the relationship of p=|t/h|. Such incrementsmay be possible in the aforementioned 16-bit numerical representation oft.

To leave sufficient header-room to adjust t upward to change viewingdistance, it may be desirable to normalize the [h,v,t] representation toa value that is 65535 minus the maximum addition that may still beapplied, so that the representation does not overflow when increasing t.For example, [6,1,9] may be scaled up to [43476, 7246, 65214] to leave aheadroom of ‘321’ for view distance adjustment.

Phase-to-View-Number Mapping

Having assigned the phase to the pixels and sub-pixels of the pixelgrid, view numbers may be assigned based on the phases, which may thenbe used to interleave the image data of views. FIG. 2B illustrates suchdisplay of interleaved image data 260 of views in which sub-pixels areshown having an intensity (and color) which corresponds to that of theassigned image data. FIG. 2B further shows the view numbers which wereused for the interleaving, while FIG. 2C shows the (upscaled) phases 280on the basis of which the view numbers of FIG. 2B were assigned.

It is noted that even though the number of phases may be (potentiallyvastly) larger than the number of views compared to a situation in whichthere is a 1:1 relation between phase and view number, it is typicallynot desired to render or otherwise obtain unique views of the scene foreach of these phases. As such, the number of views is typically muchlower, and may be determined by factors such as the number ofinstantiated rendering pipelines, etc. For example, as also shown inFIG. 2A, there may be 9 unique views 0-8 for which image data may beavailable or may be generated. As such, phases may have to be mapped toa limited set of view numbers.

There are various options and considerations when mapping the determinedphase to a view number. For example, one may consider that a large partof a viewing cone is used for stereoscopic viewing. A smaller part, forexample a quarter to a third of the viewing cone, may be used forso-called pseudoscopic viewing to reduce artifacts in the transitionarea between cones. The purposeful generation of a pseudoscopic viewingzone is known per se, for example from WO 2013/102500 A1.

In the example of having 9 phases, one may assign view numbers 0, 1, 2,3, 4, 5, 6, 4, 2 to the 9 phases to establish both a stereoscopicviewing part (from 0 to 6) and a pseudoscopic viewing part (e.g., 6, 4,2, 0), thereby assigning 7 unique view numbers to the 9 phases. In theexample of an ‘upscaled’ representation to [12, 2, 18], one may assignview numbers 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 5, 4, 3, 2, 1 to the18 phases, thereby yielding a finer view distribution in thepseudoscopic area. However, also this example only assigns 7 unique viewnumbers. In the [12, 2, 18] example, only even phases are assigned,e.g., based on the horizontal delta h and the vertical delta v beingeven numbers. As such, the view numbers which are assigned correspond tothose of the abovementioned ‘9 phase’ example. The odd phases in thephase-to-view mapping may nevertheless be used, for example for pitch orslant corrections.

An example for the phase-to-view mapping 300 for 64 phases is shown inFIG. 3, where the phase 310 is set out on the horizontal axis againstthe view number 320 on the vertical axis. As can be seen in FIG. 3,every view number is repeated three times in the pseudo-stereoscopicarea 350, and 5 times in the stereoscopic area 330, with the outer views0 and 8 being assigned 4 phases.

Rather than repeating views in the phase-to-view mapping, one may alsouse a fixed-point representation for view numbers and thus representview numbers with an increased precision, e.g., with view number 1.5representing an intermediate view between view 1 and 2, or in general,such views representing ‘inter-view’ positions. In such cases,interpolation may be applied to the image data of the neighboring views,e.g., views 1 and 2, to compute the image data to be displayed at suchan inter-view position. Alternatively, the view rendering may beperformed at a higher precision or ‘on demand’ for the inter-viewdirection of a display element.

The phase-to-view mapping may be generated and/or implemented in variousways. In general, a high bit precision, such as 16-bit, may be desirablefor accurately accumulating the phase deltas over, for example, the 2160lines and 3840 pixels of a 4K panel. However, only the most significantbits of the numerical representation of the determined phase may beneeded to determine the view number, given that the phases are typicallyonly mapped to a relatively small number of views.

A specific example may be the following. When a [h,v,t] approach is usedwhich is up-scaled to t≈65215 (or slightly less), while allowing for tto be view distance adjusted to the range of 65025−65535 (or slightlyless), then the value of the most significant byte of t (so discardingthe least significant byte) is between 254 and 255, and thecorresponding phases between 0 and 255. This yields enough precision forup to several tens of views. For a low number of views, even fewerphases are needed, as for example indicated in FIG. 3 where already manyviews are repeated in the phase-to-view mapping even for 6-bits ofprecision (64 phases). One may thus compute the phase-to-view mappingfor each of the possible values for the upper bits of t and store thesein a look-table. The variations in the value of the most significantbyte of t due to view distance adjustment are only 1 in 256, so may beignored.

Given the above, the phase-to-view mapping may be implemented as alook-up table using only the upper bits of the phase as index to thetable.

Such a look-up table may be partly or entirely programmable, forexample, using an external interface. An entirely programmable look-uptable may enable arbitrary and/or ‘exotic’ phase-to-view mappings to beimplemented, for example, which deviate from linear stereoscopic andpseudo-stereoscopic phase-to-view relations. Another example is that alimited number of pre-programmed look-up tables may be implemented whichmay be selectable, e.g., at manufacture or during use (at run-time). Alook-up table may also allow fractional view numbers to be programmed.Another example is that the look-up table may only be programmed withvalues that directly correspond to integer view numbers, e.g., with allfractional bits set to 0.

With further reference to the look-up table, one may consider that themost-significant bits of the phase may be used to index the look-uptable to determine the view number for a particular display element, andthat the remaining bits are not used for determining the view number. Inanother embodiment, one may distinguish between three classes: theupper-most bits of the numerical representation of the phase which maybe are used as index to the look-up table, the lower-most bits that arenot used to determine the view number, and the remaining bitsin-between. These ‘intermediate’ bits may be used to interpolate betweenthe neighboring entries in the phase-to-view table. For example, if theupper-most bits indicate that view 4 is to be indexed, and theintermediate bits indicate a fraction ¾, then (when using linearinterpolation), ¾ of the phase-to-view entry at index 5 may be added to¼ of the phase-to-view entry at index 4 to arrive at the view number.Next to linear interpolation, also higher-order interpolation may beused to interpolate between the entries containing view numbers in thelook-up table, for example using splines as known per se in the art. Ina particular embodiment of this approach, the look-table may beimplemented as a 1D texture map, and texture units of the processorsystem may be configured to perform interpolation when retrieving theview number for the phase corresponding to each subpixel.

It is noted that the above refers to ‘bits’ but may equally apply to anytype of numerical digits of a particular numerical representation of thephase.

Processor System and Computer-Implemented Method

The above-described embodiments may be carried out by means of anappropriately configured processor system. FIG. 1 shows such a processorsystem as an external component providing interleaved image data to the3D display.

FIG. 4 shows an alternative to FIG. 1, in which the processor system 120is implemented in the form of an internal component of the 3D display140 internally outputting data 122 of the interleaved output image. FIG.4 also shows internal components of the processor system 120, such asthe processor 130 and the memory 135. Non-cited reference numerals inFIG. 4 correspond to those of FIG. 1. Although not shown explicitly inFIGS. 1 and 4, the processor system 120 may also have an interface forallowing the horizontal delta h, the vertical delta v and/or the totalnumber of phases t to be externally configured, and/or the sub-pixeloffsets. Such an interface may take various forms, such as electricalinterfaces such as I2C and RS232, software interfaces such as softwareAPIs (Application Programming Interfaces), or the combination of both.For example, the interface may be a software API for a driver, which maythen communicate via 120 to set values in hardware registers thatcorrespond to the different items. Additionally or alternatively, suchan interface may allow the values of the pitch distance p and the slantangle s to be externally configured, with the processor system thendetermining values of the horizontal delta h, the vertical delta vand/or the total number of phases t based on the values of p and s.

It will be appreciated that the processor system 120 may not need tointerleave image data and output the interleaved output image. Rather,embodiments are conceived where the processor system 120 assigns theview numbers and where another entity interleaves the image data basedon the assigned view numbers.

In general, the processor system may be embodied in or as a separatedevice, e.g., in or as a set-top box, personal computer, gaming consoleor similar device that is connectable to the 3D display. In general, theprocessor system may be implemented by a device or apparatus. The deviceor apparatus may comprise one or more (micro)processors which executeappropriate software. Software implementing the functionality of thefunction(s) may have been downloaded and/or stored in a correspondingmemory or memories, e.g., in volatile memory such as RAM or innon-volatile memory such as Flash. Alternatively, the function(s) of theprocessor system may be implemented in the device or apparatus in theform of programmable logic, e.g., as a Field-Programmable Gate Array(FPGA), or as an Application-Specific Integrated Circuit (ASIC), or asany other type of circuit or combination of circuits.

FIG. 5 shows a computer-implemented method 400 of assigning view numbersto display elements of an autostereoscopic display for use ininterleaving image data of different viewpoints of a scene on the basisof said assigned view numbers. The computer-implemented method 400 may,but does not need to, correspond to an operation of the processor system120 as described with reference to FIG. 1, 4 and others. The method 400may comprise, in a step titled “DETERMINING PHASE OF DISPLAY ELEMENT”,determining 410 a phase for a respective display element to be used inthe assignment of the view number, e.g., in a manner as described above.The method 400 may further comprise, in a step titled “DETERMINING VIEWNUMBER FROM DETERMINED PHASE”, determining 420 the view number from saiddetermined phase, e.g., in a manner as described above.

The method 400 may be implemented on a processor system, e.g., on acomputer as a computer implemented method, as dedicated hardware, or asa combination of both. As also illustrated in FIG. 6, instructions forthe computer, e.g., executable code, may be stored on a computerreadable medium 450, e.g., in the form of a series 460 of machinereadable physical marks and/or as a series of elements having differentelectrical, e.g., magnetic, or optical properties or values. Theexecutable code may be stored in a transitory or non-transitory manner.Examples of computer readable mediums include memory devices, opticalstorage devices, integrated circuits, servers, online software, etc.FIG. 6 shows an optical disc 450.

In another embodiment, the computer readable medium 450 may comprise thelook-up table as described above as transitory or non-transitory data.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.Expressions such as “at least one of” when preceding a list or group ofelements represent a selection of all or of any subset of elements fromthe list or group. For example, the expression, “at least one of A, B,and C” should be understood as including only A, only B, only C, both Aand B, both A and C, both B and C, or all of A, B, and C. The inventionmay be implemented by means of hardware comprising several distinctelements, and by means of a suitably programmed computer. In the deviceclaim enumerating several means, several of these means may be embodiedby one and the same item of hardware. The mere fact that certainmeasures are recited in mutually different dependent claims does notindicate that a combination of these measures cannot be used toadvantage.

1. A computer-implemented method of assigning view numbers to displayelements of an autostereoscopic display for use in interleaving imagedata of different viewpoints of a scene on the basis of said assignedview numbers, the autostereoscopic display comprising: a display panelcomprising an array of display elements; and an array of elongatedoptical elements for redirecting light emitted by the display elementsin mutually different directions, the optical elements being arrangedsubstantially in parallel at a pitch distance p and oriented with theirmain longitudinal axis at a slant s to a column direction of the arrayof display elements, the method comprising: determining a phase for arespective display element to be used in the assignment of the viewnumber, wherein the phase is representative of a relative horizontalposition of the respective display element with respect to an opticalelement redirecting the light emitted by the respective display elementand is thereby indicative of a direction in which the light isredirected, wherein the phase is determined as a delta with respect tothe phase of a preceding display element at a horizontal position x anda vertical position y in the array of display elements in accordancewith:phase(x+1,y)=(phase(x,y)+h)% tphase(x,y+1)=(phase(x,y)+v)% t wherein h represents a horizontal deltain phase per display element, wherein v represents a vertical delta inphase per display element, wherein t represents a total number of phasesand wherein % is a functional representation of a modulo operation,wherein values of h, v and t are selected as integer values whichapproximate the pitch distance p and the slant s in accordance with$p \approx {{\frac{t}{h}}\mspace{14mu}{and}\mspace{14mu} s} \approx \frac{v}{h}$so that the approximation error in the phase over the width and heightof the array of display elements accumulates to less than the pitchdistance p; and determining the view number from said determined phasebased on a number of most significant digits of a numericalrepresentation of the phase.
 2. The method according to claim 1, furthercomprising selecting the values of h, v and t by: approximating thepitch distance p and the slant s as rational numbers having a commondenominator; determining the value of h as being the common denominator;determining the value of v by multiplying s by h and rounding a resultof said multiplication to obtain an integer value for v; and determiningthe value of t by multiplying p by h and rounding a result of saidmultiplication to obtain an integer value for t.
 3. The method accordingto claim 1, further comprising selecting the value of h, the value of vand the value of t so that a largest one of said values is a maximumvalue of the numerical representation of the phase.
 4. The methodaccording to claim 1, further comprising selecting the value of h, thevalue of v and the value of t so that a largest one of said values plusa headroom value equals the maximum value of the numericalrepresentation of the phase, wherein the headroom value represents anallocation of a headroom with respect the maximal value for allowingadjustments of t for adjusting for the view distance of a viewer to theautostereoscopic display.
 5. The method according to claim 1, whereinthe display elements are pixels or group of pixels, wherein each pixelcomprises a number of sub-pixels, and wherein the method furthercomprises assigning a sub-pixel phase to a respective sub-pixel byadding an offset to, or subtracting an offset from, the determined phaseof the pixel or group of pixels.
 6. The method according to claim 1,wherein determining the view number from the determined phase comprisesusing the number of most significant digits of the numericalrepresentation of the phase as an argument to a function providing amapping from the determined phase to the view number, for example as anindex to a look-up table.
 7. The method according to claim 6, whereinthe look-up table defines, for increasing phases, a stereoscopicsequence of views in which the view numbers increase and a pseudoscopicsequence of views in which the view numbers decrease.
 8. The methodaccording to claim 6, wherein the look-up table contains integerrepresentations of the view numbers.
 9. The method according to claim 6,further comprising selecting the look-up table from a number of look-uptables, each look-up table providing a different mapping from thedetermined phase to the view number.
 10. The method according to claim1, further comprising adjusting for the view distance of a viewer to theautostereoscopic display by adjusting the value of t.
 11. A computerreadable medium comprising transitory or non-transitory datarepresenting instructions for a processor system to perform the methodaccording to claim
 1. 12. A non-transitory computer readable mediumcomprising data representing the look-up table according to claim
 6. 13.A processor system for assigning view numbers to display elements of anautostereoscopic display for use in interleaving image data of differentviewpoints of a scene on the basis of said assigned view numbers, theautostereoscopic display comprising: a display panel comprising an arrayof display elements; and an array of elongated optical elements forredirecting light emitted by the display elements in mutually differentdirections, the optical elements being arranged substantially inparallel at a pitch distance p and oriented with their main longitudinalaxis at a slant s to a column direction of the array of displayelements, the processor system comprising: a memory comprisinginstruction data representing a set of instructions; a processorconfigured to communicate with the memory and to execute the set ofinstructions, wherein the set of instructions, when executed by theprocessor, cause the processor to determine a phase for a respectivedisplay element to be used in the assignment of the view number, whereinthe phase is representative of a relative horizontal position of therespective display element with respect to an optical elementredirecting the light emitted by the respective display element and isthereby indicative of a direction in which the light is redirected,wherein the phase is determined as a delta with respect to the phase ofa preceding display element at a horizontal position x and a verticalposition y in the array of display elements in accordance with:phase(x+1,y)=(phase(x,y)+h)% tphase(x,y+1)=(phase(x,y)+v)% t wherein h represents a horizontal deltain phase per display element, wherein v represents a vertical delta inphase per display element, wherein t represents a total number of phasesand wherein % is a functional representation of a modulo operation,wherein values of h, v and t are selected as integer values whichapproximate the pitch distance p and the slant s in accordance with$p \approx {{\frac{t}{h}}\mspace{14mu}{and}\mspace{14mu} s} \approx \frac{v}{h}$so that the approximation error in the phase over the width and heightof the array of display elements accumulates to less than the pitchdistance p; and determine the view number from said determined phasebased on a number of most significant digits of a numericalrepresentation of the phase.
 14. The system according to claim 13,further comprising a configuration interface for enabling the value ofthe horizontal delta h, the vertical delta v and/or the total number ofphases t to be externally configured.
 15. The system according to claim13, further comprising a configuration interface for enabling the valuesof the pitch distance p and the slant s to be externally configured,wherein the set of instructions, when executed by the processor, causethe processor determine the values of the horizontal delta h, thevertical delta v and/or the total number of phases t based on the valuesof p and s.